1. Field of the Invention
The invention relates to a plastic sheet, in particular for lining construction elements formed of cementitious material such as concrete, which is preferably made of thermoplastic and is provided with attachments on one side thereof. Protection sheets made of plastic, so-called knubbed sheets, are used in particular in concrete tank construction in cases where it is necessary to produce liquid-tight, gas-tight, chemically resistant tanks. The plastic sheets form the lining of such tanks; they provide the resistance to the chemicals and liquids. The mechanical strength of the entire structure is essentially provided by the concrete structure. In general, the bonding of the plastic sheets to the concrete structure poses difficulties, since a smooth plastic sheet does not form a firm mechanical bond to the concrete. The assistance of adhesives does not provide long-term satisfactory results.
For these reasons, various anchoring elements, including those with undercuts, have been proposed. These anchoring elements are attached to one side of the plastic sheet and, during the production of the tank, are embedded in the surface of the concrete to be protected, typically the inner surface. The desired firm bond between the plastic sheet and concrete structure can be achieved in this manner.
2. Description of the Related Art
European Patent Application 436 058 A1 teaches an economically desirable process for producing knubbed sheets from plastic, and a knubbed sheet of this kind. This relates in particular to the integral production of plastic sheets having undercut knubs, which have thoroughly proven their desirability.
However, it has been found that such plastic sheets, which generally consist of dark to black plastic, require special precautions on the construction site. In particular, during installation in the concrete structure, relatively high thermal expansion occurs, for example when they are installed under direct sunlight. This expansion must be anticipated. The plastic sheets are nailed to the formwork of the concrete structure and then have to be protected against direct sunlight to prevent the excessive thermal expansion. In addition, mechanical damage to these plastic sheets, even when they are installed, can only be recognized with great difficulty. In the interests of safety, however, such damage must be repaired as soon as practicable.